As someone who's just published a book, I'm keenly aware that the negative reviews that hurt the most are those by critics who begin by saying that, up until now, they have been huge admirers of your work. After all, if the book in question doesn't even appeal to your biggest fans, who else is going to stomach it? I'd much rather get a bad review from someone who states at the outset that he hates everything I've ever done.

With this in mind, I'm loathe to admit that I'm a fan of Terry Johnson's. Hitchcock Blonde, his last play at the Court, was an insightful and hilarious investigation of the male "gaze", while his film for television about Peter Cook and Dudley Moore, Not Only But Always, was a genuine delight. Alas, Piano/Forte isn't in the same class.

It begins promisingly enough, with the wayward daughter of a disgraced Tory MP arriving at the family home in order to disrupt her father's forthcoming nuptials to a Page Three girl. When it emerges that the two lovebirds met on I'm A Celebrity...Get Me Out of Here, the stage is set for a scabrous send-up of our fame-obsessed society.

Unfortunately, Johnson quickly loses interest in this subject--or, at least, discovers he has nothing original to say about it--and returns to his perennial theme, namely, sex. Like the late Dennis Potter, Johnson is preoccupied with the sexual attraction that exists between young women and middle-aged men, but this topic was dealt with much more successfully in Hitchcock Blonde, not least because Piano/Forte isn't nearly as funny.

Presumably, the reason the ex-Tory MP has taken up with a woman less than half his age is because he harbours an unconscious desire for his daughter--not hard to understand when she's played by Kelly Reilly--and the feeling appears to be mutual because his daughter's way of greeting her father when he arrives with his bride-to-be is to parade around the house topless. In case we're in any doubt about the daughter's feelings, we also discover that she has had sex with her uncle, the proxy head of the household when her father's not around.

Johnson's mistake is to take this naturally comedic material--think how skilfully the same subject-matter is handled in The Philadelphia Story--and try to turn it into the stuff of high drama. O'Neill pulled it off in Mourning Becomes Electra, but Johnson doesn't have the same gift for melodrama as he does for comedy. Piano/Forte seems to lose momentum as it progresses, with witty one-liners gradually giving way to rambling, portentous monologues, until you find yourself willing the curtain to come down. It's not boring, exactly, it is just painful in a way that Johnson can't have intended.

Still, Piano/Forte is a lot easier to sit through than The Alchemist, a modern-dress version of the famous Ben Jonson comedy about a trio of 17th Century con artists. In theory, this production should have been solid as rock. Not only is it directed by Nicholas Hytner, who's usually pretty dependable when it comes to staging Elizabethan plays, but it stars Simon Russell Beale, Alex Jennings and Lesley Manville, three of Britain's best stage actors. So why is it so sleep-inducingly dull?

One reason is that its constant straining for contemporary relevance quickly begins to pall. Hytner homes in on as many fashionable targets as he can--at one stage, Jennings poses as an American New Age guru--but the overall effect is to convince you that he doesn't have much faith in the original text. Having said that, Hytner's lack of confidence turns out to be justified. At the risk of sounding like a philistine, The Alchemist is one of those plays that is probably better studied than seen. The language is so dense and impenetrable that unless you're paying rapt attention the plot is incredibly hard to follow--and once you've lost the thread it's impossible to pick it up again. Not only that, but it's a farce that becomes less, rather than more, funny as the evening wears on. Even the normally sycophantic first night audience at the National, who always laugh loudly at the feeblest of witticisms to demonstrate that they've "got" the joke, struggled to find the on-stage hi-jinks funny. This one is strictly for hard-core Jonson fans, I'm afraid, though Hytner will be relieved to learn that I find almost all of Jonson's stuff unwatchable.